The present invention relates to a tire with radial carcass reinforcement, intended to support heavy loads, to be inflated to very high pressures and to run at high speed, requisites of a tire for an airplane.
A tire of this kind generally comprises radial carcass reinforcement composed of textile reinforcing elements which make an angle which may be between 80.degree. and 100.degree. to the circumferential direction, said plies being anchored into each bead at one or more bead wires.
The carcass reinforcement is radially surmounted by a crown reinforcement generally composed of a number of plies, some formed of textile reinforcing elements constituting the so-called working crown plies and others, radially on the outside, formed of reinforcing elements that undulate within the plane of the ply, generally made of metal, said others constituting the so-called protective crown plies because they have the function of protecting the underlying textile crown reinforcement from attack from the ground. Crown reinforcement of this kind is described in French patent FR 2 499 475, the working crown reinforcement mainly consisting of plies of textile cords oriented circumferentially, it being possible that said plies may be supplemented by plies of textile cords which are steeply inclined with respect to the circumferential direction, it being possible for the angle of inclination to be between 30.degree. and 90.degree. and it being possible for said plies to lie radially above or below the plies of circumferential cords.
Although remarkable in terms of high-speed endurance, the treads of the tires described hereinabove dc not give satisfactory resistance to wear, this resistance generally being measured by the number of landings that can be performed. For ten years or so the assignee company has been using another structure of working crown reinforcement, this being composed of a number of layers of textile reinforcing elements obtained by winding a strip of one or more continuous elements in a path extending from one edge of the crown reinforcement to the other (a so-called zig-zag path), the angle with respect to the circumferential direction taken by said reinforcing elements being small. Known since the 1960's, this principle, like in the case of crown plies which are said to be folded back on themselves, makes it possible to avoid having the free ends of the reinforcing elements at the edges of the plies. Such examples of crown reinforcements are described, for example, in patent GB 890 648 or, more recently, in patent U.S. Pat. No. 4,838,966.
The plies obtained by winding a strip from one edge of the crown reinforcement to the other will be called zig-zag plies "guided" at an angle .alpha. with respect to the circumferential direction, abbreviated to NT.alpha..degree., keeping in mind the fact that at least two plies of reinforcing elements thus obtained are, because of the way in which they are obtained, inseparable, to form what will be called a "guided" twin zig-zag ply. The plies of continuous and circumferential reinforcing elements are also generally obtained by helical winding o f an element or a strip of several reinforcing elements, but it is possible to use just one ply of reinforcing elements. They will be called plies "guided" at 0.degree., abbreviated to NT0.degree.. All of said plies which are "guided" at an angle and at 0.degree. have the distinguishing feature that they have only a few cut elements, two if the winding relates merely to one reinforcing element, and twice the number of elements forming the strip if the winding involves a strip.
Combining "guided" zig-zag plies NT.alpha..degree. formed of oriented continuous cords either with other plies "guided" at an angle or with plies of circumferential cords NT0.degree., provides, for an airplane tire, a crown reinforcement which is a very good compromise between the mass of the reinforcement and performance, particularly in terms of running speed and in terms of wear.
Also, depending on the dimensions and the running conditions, an airplane tire may have a crown reinforcement composed, for example, of seven plies of reinforcing elements and consisting, working radially from the inside outward,
either of 6 NT.alpha..degree. (in the form of 3 twin zig-zag plies) and one NT0.degree., PA1 or 4 NT.alpha..degree. (in the form of 2 twin zig-zag plies), one NT0.degree. and 2 NT.alpha..degree. (in the form of a twin zig-zag ply), PA1 or 4 NT.alpha..degree. (in the form of 2 twin zig-zag plies) and 3 NT0.degree., PA1 or 3 NT0.degree. and 4 NT.alpha..degree., PA1 or 2 NT.alpha..degree. (in the form of one twin zig-zag ply), one NT0.degree. and 4 NT.alpha..degree. (2 twin zig-zag plies), PA1 or 2 NT.alpha..degree. (1 twin zig-zag ply), 3 NT0.degree. and 2 NT.alpha..degree., PA1 or 2 NT.alpha..degree. (1 twin zig-zag ply) and 5 NT0.degree., PA1 or 5 NT0.degree. and 2 NT.alpha..degree. (1 twin zig-zag ply), PA1 or 1 NT0.degree. and 6 NT.alpha..degree. (3 twin zig-zag plies).
The crown reinforcements described hereinabove, which are relatively massive, under certain running conditions, particularly at instantaneously very high speeds and overloads, prove too rigid and not strong enough, which leads to unsatisfactory endurance.